On Thu, May 27, 2021 at 07:08:04PM -0400, Felix Kuehling wrote:

Now we're trying to migrate data to and from that memory using the
migrate_vma_* helpers so we can support page-based migration in our
unified memory allocations, while also supporting CPU access to those
pages.

So you have completely coherent and indistinguishable GPU and CPU
memory and the need of migration is basicaly alot like NUMA policy
choice - get better access locality?
 

This patch series makes a few changes to make MEMORY_DEVICE_GENERIC pages
behave correctly in the migrate_vma_* helpers. We are looking for feedback
about this approach. If we're close, what's needed to make our patches
acceptable upstream? If we're not close, any suggestions how else to
achieve what we are trying to do (i.e. page migration and coherent CPU
access to VRAM)?

I'm not an expert in migrate, but it doesn't look outrageous.

Have you thought about allowing MEMORY_DEVICE_GENERIC to work with
hmm_range_fault() so you can have nice uniform RDMA?

People have wanted to do that with MEMORY_DEVICE_PRIVATE but nobody
finished the work

Jason